Answer

(a) The three cube roots are:
$2~(cos~90^{\circ}+i~sin~90^{\circ})$
$2~(cos~210^{\circ}+i~sin~210^{\circ})$
$2~(cos~330^{\circ}+i~sin~330^{\circ})$
(b) We can see the three vectors in the complex plane: